The invention relates to a method for producing a housing for a throttle valve connection piece, which housing has a throttle orifice for a throttle valve, the housing being produced from plastic by the injection molding method, and, during the injection molding method, plastic being partially injected around a metal cylinder which, at least in the region of the throttle valve, forms the throttle orifice. The invention relates, furthermore, to a throttle valve connection piece with a housing which has a throttle orifice for a throttle valve, the housing produced from plastic by the injection molding method having a metal cylinder which is partially surrounded by plastic and, at least in the region of the throttle valve, forms the throttle orifice.
Throttle valve connection pieces are conventionally used for controlling the fresh-gas quantity of a motor vehicle. Throttle valve connection pieces comprise a housing with a throttle orifice and a throttle member arranged in the throttle orifice. The throttle member assumes a specific position in the throttle orifice for the passage of a specific fresh-gas quantity. For this purpose, the throttle member can be activated mechanically or electronically.
Housings of throttle valve connection pieces are usually produced from plastic or from metal. Those housings of throttle valve connection pieces which are manufactured from metal, for example aluminum, may have particularly low tolerances. Low tolerances are necessary for a throttle valve connection piece, in the region of the throttle valve, particularly when an especially accurate opening and closing of the throttle valve is required. In the closing region of the throttle valve, these requirements are also referred to as leakage-air requirements. However, metal housings of throttle valve connection pieces have the disadvantage that, after the housing has been produced, for example by the diecasting method, complicated remachining of the housing is necessary. It is often necessary, for example, to carry out careful remachining of the housing extensions provided for bearings of the throttle valve shaft, so that the bearings of the throttle valve shaft can be fitted into the housing without tilting.
Those housings of throttle valve connection pieces which are manufactured from plastic have a lower weight than those housings of throttle valve connection pieces which are manufactured essentially from metal, in particular aluminum. Furthermore, plastic, as material, can also be adapted in an especially simple way to a wide variety of geometric configurations of the housing. Moreover, in the case of plastic housings produced by the injection molding method, inserts, for example bearings for mounting the throttle valve shaft, can be injected into the housing.
However, those housings of throttle valve connection pieces which are produced from plastic by the injection molding method have the disadvantage that they shrink during and after the injection molding method. Moreover, housings of this type may experience warping after removal from the mold, that is to say may be deformed when they are taken out of the injection mold. Also, those housings of throttle valve connection pieces which are manufactured from plastic are not especially dimensionally stable over a particularly wide temperature range. On the one hand, in a motor vehicle, housings of throttle valve connection pieces are exposed to outside temperatures down to xe2x88x9240xc2x0 C. On the other hand, when the throttle valve connection piece is in operation, the temperature of the throttle valve connection piece may rise above 100xc2x0 C. These wide temperature fluctuations may lead to adverse deformations of the plastic in the pivoting region of the throttle valve. These deformations, in turn, may lead to the particularly high accuracy of fit of the throttle valve in the housing decreasing in the course of time. In this context, particularly high accuracy of fit means, for example, accuracies of fit of the housing of the throttle valve connection piece in the range of 0 to 30 xcexcm, in so far as the housing is subject, for example, to the ISO tolerance with respect to the dimension for the throttle orifice. As a result of changes in shape of the throttle orifice, the particularly stringent leakage-air requirements, especially when the throttle valve is in the idling position, can no longer be satisfied. This entails an increased fuel consumption and a diminished exhaust-gas quality. For a constant fuel consumption and a constant exhaust-gas quality, therefore, it is necessary to have a dimensional stability of the housing of the throttle valve connection piece, in particular of the throttle orifice, over many years.
DE 43 34 180 A1 discloses a housing manufactured from plastic for a throttle valve connection piece, an annular insertion part being integrated into said housing in the pivoting region of the throttle valve. Although the insertion part, around which plastic is injected completely, improves dimensional stability of the housing of the throttle valve connection piece, it cannot reliably prevent changes in shape in the pivoting region of the throttle valve due to the high compressive loads during the injection of the plastic. Interaction of the medium passing through the throttle valve connection piece with the plastic leads, as before, to changes in shape of the plastic and therefore of the throttle orifice, even though these changes are no longer as drastic as would be the case without the annular insertion part.
The object on which the invention is based, therefore, is to specify a method for producing a housing for a throttle valve connection piece of the abovementioned type, in which the dimensional stability of the metal cylinder during the injection molding method and the dimensional stability of the housing after removal from the mold are ensured in an especially reliable way. Moreover, a throttle valve connection piece is to be specified, the housing of which has especially high dimensional stability even in the case of especially high temperature fluctuations.
With regard to the method, this object is achieved, according to the invention, in that, before the injection molding method, an expanding mandrel having a diameter which can be enlarged is expanded against the inner face of the metal cylinder. During the injection molding method the inner face if the metal is supported at least partially by the expanding mandrel, and, after the injection molding method, the outer circumference of the expanding mandrel is reduced in order to remove the expanding mandrel from the interior of the metal cylinder.
The invention proceeds from the notion that dimensional stability of the housing after removal from the mold is ensured particularly reliably when the housing has dimensionally stable elements in the region of the throttle orifice during the injection molding operation. A particularly simple design of a dimensionally stable element, at least for a part region of the throttle orifice, is a metal cylinder which is hollow on the inside. It must be remembered, in this case, however, that, during the injection molding method, even a metal cylinder must be protected against deformations which may occur due to the pressure built up by the plastic during the injection molding method. The problem arises here, however, that supporting bodies which support the metal cylinder during the injection molding method often leave behind scores or roundnesses in the metal cylinder during removal from the mold. Scores or roundnesses normally occur when the supporting body is moved out of the metal cylinder, particularly when the supporting body is released from the inner casing of the metal cylinder. The result of these scores or roundnesses may be that the housing of the throttle valve connection piece does not have, for example, a tolerance which is predetermined for the throttle orifice. These scores or roundnesses can be removed by means of a subsequent mechanical machining of the housing, which, however, proves highly time-intensive and markedly increases the outlay involved in producing the housing. A supporting body which supports the metal cylinder during the injection molding method does not leave behind any scores or roundnesses in the housing when the supporting body expands against the housing during the injection molding method and can be reduced in respect of its outer dimensions during removal from the mold. An expanding mandrel has this property of having larger dimensions during the injection molding method than during removal from the mold. In order to produce, for a throttle valve connection piece, a housing having virtually no scores and roundnesses, therefore, the expanding mandrel is pushed into the interior of the metal cylinder before the injection molding method and expanded against the inner casing of the metal cylinder. During removal from the mold, the outer circumference of the expanding mandrel is then first reduced, before the expanding mandrel is removed from the interior of the metal cylinder.
Advantageously, the expanding mandrel has an expanding device and an outer casing at least partially surrounding the expanding device. Before the injection molding method, the outer casing of the expanding mandrel is then expanded radially against the inner face of the metal cylinder by means of the expanding device. During the injection molding method, the outer casing of the expanding body is expanded radially against the inner face of the metal cylinder by means of the expanding device. After the injection molding method, a contraction of the outer casing of the expanding mandrel is carried out by means of the expanding device in order to remove the expanding mandrel from the interior of the metal cylinder. An expanding mandrel with an outer casing at least partially surrounding the expanding device can be expanded radially and contracted radially, with the result that the function of the expanding mandrel is ensured in an especially simple way by means of a particularly small number of elements. Expansion and contraction of the expanding device take place mechanically or hydraulically in this case.
During the injection molding method, the outer casing of the expanding mandrel is advantageously pressed at least partially over its area onto the inner face of the metal cylinder by the expanding device of the expanding mandrel. The outer casing of the expanding mandrel is therefore shaped in such a way that it can be expanded over its area onto the inner face of the metal cylinder by means of the expanding device, with the result that the expanding mandrel can exert a particularly homogeneous pressure on the inner face of the metal cylinder. Support of the metal cylinder is thereby ensured in a particularly reliable way, even when the throttle orifice has different shapes, scores and/or roundnesses caused by the outer casing of the expanding mandrel being reliably avoided. There is therefore no need for remachining of the metal cylinder after the injection molding method, with the result that the outlay in terms of the production of the housing of the throttle valve connection piece is particularly low. If in this case, for example, the expanding mandrel has an oval contour, the metal cylinder can have generated on it an intentional nonroundness which is compensated by the shrinkage of the plastic during solidification. At the same time, by means of the mechanical or hydraulic expanding device, an approximately homogeneous pressure of the outer casing of the expanding mandrel is exerted on the inner face of the metal cylinder.
Advantageously, the expanding device has an axle, a securing means and a supporting body, the supporting body being movable along the axle, having an approximately rotationally symmetric shape, tapering along the axle and having a first end region with a smaller diameter and a second end region with a larger diameter. Before the injection molding method, in order to expand the outer casing of the expanding mandrel against the inner face of the metal cylinder, the supporting body is moved, with its first end region, having a smaller diameter, along the axle into the interior of the metal cylinder. During the injection molding method, the supporting body is fixed on the axle by the securing means. After the injection molding method, in order to remove the supporting body from the interior of the metal cylinder, a contraction of the outer casing of the expanding mandrel is carried out by means of a movement of the supporting body along the axle out of the interior of the metal cylinder. Due to the shape and movability of the supporting body, the expanding device and consequently the expanding mandrel can be adapted in an especially simple way to different heights of the metal cylinder. Moreover, the movement of the tapering supporting body proves to be sufficient to expand the expanding mandrel against the inner face of the metal cylinder in the interior of said metal cylinder.
The supporting body of the expanding device is advantageously designed approximately in the form of a cone. A cone can be produced particularly simply, and, in the case of the cone, said cone can be adapted especially simply to different diameters and different shapes of the throttle orifice by means of the inclination of the outer face relative to the base.
The axle advantageously has a thread, onto which the securing means is screwed in order to fix the supporting body. When the securing means is designed, for example, as a nut to be screwed onto a thread, the pressure to be exerted on the outer casing of the expanding mandrel can be set in particularly fine steps by means of a specific number of turns of the nut on the thread.
Advantageously, the supporting device has, in addition to the first supporting body, a second supporting body which is fixedly connected axially to the axle, has an approximately rotationally symmetric shape, tapers along the axle and has a first end region with a smaller diameter and a second end region with, in comparison with this, a larger diameter. Before the injection molding method, in order to expand the outer casing of the expanding mandrel against the inner face of the metal cylinder, the first end region, having a smaller diameter, of the first supporting body is then moved into the interior of the metal cylinder in the direction of the first end region, having a smaller diameter, of the second supporting body. During the injection molding method, the first supporting body is then fixed on the axle by the securing means. After the injection molding method, in order to remove the expanding mandrel from the interior of the metal cylinder, a contraction of the outer casing of the expanding mandrel is carried out by means of a movement of the first end region, having a smaller diameter, of the first supporting body along the axle, away from the first end region, having a smaller diameter, of the second supporting body, out of the interior of the metal cylinder. In this case, advantageously, the second supporting body is designed approximately in the form of a cone. A first and a second supporting body of the expanding device can be adapted in an especially simple way to different axle lengths of the outer casing of the expanding device and therefore to different axle lengths of the metal cylinder. Moreover, due to the tapering shape both of the first and of the second supporting body, the pressure which the two supporting bodies exert jointly on the outer casing of the expanding mandrel can be set especially simply. In particular, by means of two approximately conical supporting bodies, a particularly homogeneous pressure can be exerted on the inner face of the metal cylinder by means of an approximately cylindrical outer casing of the expanding device. In this case, the first supporting body and the second supporting body may either have the same cone-like shape or else have different outer contours of their approximately conical configuration.
As regards the throttle valve connection piece, the object is achieved, according to the invention, in that, in order to seal off the housing together with the metal cylinder, the metal cylinder tapers toward one or toward both of its end regions. By virtue of this refinement, the metal cylinder forming the throttle orifice at least in the region of the throttle valve can be adapted particularly well, by expansion after the injection molding method, to the remaining throttle orifice housing wall formed from plastic. This applies, in particular, when there is provision for shrinkage of the plastic in the end regions of the metal cylinder. A virtually continuous transition from the metal cylinder to the plastic of the housing is thereby ensured in the throttle orifice. When the throttle valve connection piece is in operation, a particularly smooth surface with virtually no unevennesses ensures an especially turbulence-free flow of the medium passing through the throttle orifice, with the result that a particularly high flow velocity of the medium can be achieved. A particularly high flow velocity of the medium passing through the throttle orifice when the throttle valve connection piece is in operation ensures, in turn, particularly fine regulatability of the mass flow passing through the throttle orifice.
Advantageously, the metal cylinder has extensions which project radially from its outer lateral surface and which are advantageously provided for bearings of the throttle valve shaft. These receptacles ensure in a particularly reliable way a centric fit of the throttle valve shaft in the metal cylinder. Moreover, the final mounting of the throttle valve connection piece becomes especially simple as a result, since additional receptacles for the bearings do not have to be fitted into the housing. Furthermore, the integration of the extensions into the metal cylinder reduces the elements necessary for the housing of the throttle valve connection piece, with the result that the outlay in terms of the production of the housing of the throttle valve connection piece is particularly low.
In order in an especially advantageous way to enhance the lightweight construction of the housing of the throttle valve connection piece achieved by means of the plastic, the metal cylinder is advantageously manufactured from aluminum. The housing of the throttle valve connection piece thereby has a particularly low weight.
Advantageously, the housing of the throttle valve connection piece is produced in one piece with the drive housing of the throttle valve connection piece. By virtue of this form of construction, the outlay in terms of production and assembly which is necessary for the throttle valve connection piece is particularly low.
The advantages achieved by means of the invention are, in particular, that the lightweight construction of the housing is associated with an especially high dimensional stability of the housing. At the same time, during the injection molding method, a deformation of the metal cylinder is reliably avoided by means of the expanding mandrel. During removal from the mold, the expanding mandrel is first contracted, before it is taken out of the interior of the metal cylinder. By the expanding mandrel being used, scores and/or roundnesses of the metal cylinder due to the production process are avoided in a particularly reliable way. Moreover, this production method ensures especially reliably a particularly cost-effective production of a housing for a throttle valve connection piece, this production involving a particularly low outlay in technical terms. Furthermore, a throttle valve connection piece with a metal cylinder tapering toward its end regions has an especially smooth surface of the throttle orifice, thus ensuring especially reliably a particularly turbulence-free flow of the medium passing through the throttle orifice.